Overdentures Featuring the Stress-Free Implant Modular Bar

A cost-effective option for fully edentulous patients

David R. Avery, CDT, AAS

Edentulism meets the definition of a physical impairment as set forth by the World Health Organization. The edentulous mandible presents the most significant challenge to achieving adequate masticatory function.

Increased direct-to-the-public marketing of immediate-implant restorative options has created a significant increase in requests for the procedure from fully edentulous patients. The more widespread use of implants combined with the proliferation of CAD/CAM technology application in contemporary dentistry have led to an explosion of treatment solutions available to address any situation encountered by the restorative team. While digital technology provides extraordinary accuracy and substrate integrity, the dental team should be aware of more cost-effective options, because this approach allows treatment of a much larger population segment.

An Option for Overdentures

The SFI-Bar® (stress-free bar) system is an excellent implant overdenture option. Swiss company Cendres + Metaux (www.cmsa.ch) developed the bar system, and Sterngold (www.sterngold.com) manufactures the SFI abutments, which connect to most popular implant systems. More than 4,000 SFI-Bars were placed intraorally throughout Europe and Asia between November of 2006 and April 2012 without the need for any remakes and without complications.1

The system is economically positioned between direct stud attachments and milled or SLM (selective laser melting)–fabricated bars. This article will illustrate that the SFI-Bar addresses the need for intra-implant passivity with precision-machined components, exceeding the highest metallurgical requirements.

System Components

The SFI-Bar is a modular system that connects multiple dental implants passively without soldered or laser-welded connections. The system is designed to restore the mandibular arch with two to six implants or four to six implants in the maxillae.

Finite element studies and clinical evaluation of the system have found minimal stress transmission from the prosthesis to the supporting implants under loading, with most stresses being evenly distributed between the supporting implants. Vertical loads are transmitted effectively to the supporting implants, while undesirable lateral stresses are largely eliminated.

The SFI system includes an SFI abutment implant adaptor, which adapts to the specific implant interface used. The ball joint is secured with the fixation screw into the adaptor, which supports the entire SFI-Bar assembly.

Single ball joints support the tube bar between two implants. They may compensate for angulation of 15° or a total of 30° between two implants. Double ball joints support two bars between three implants using two stems. These joints are able to support a lateral angulation from 110° to 150°. They are designed with a half-shell casing, unlike the single ball joint. They also allow vertical angulation forgiveness of 15° or a total of 30° between two implants (Figure 1).

Fixation screws secure the ball joints to the implant adaptor. They feature an internal hex of 1.32 mm and measure 5.30 mm in height. The tube bar is made of type V titanium and is 20 mm long.

Load tests conducted determined that a solution anchoring the bar on two implants can safely withstand a load of 500 N. A four-implant solution, with the bars following the alveolar ridge, can withstand a load of 1,500 N (500 N/bar).2

In addition, the SFI system includes two new female retainer part designs. Female part asymmetrical (E) is milled from Elitor® (gold alloy), which increases stability and requires minimum space for integration into the restoration, ensuring improved esthetics with various activation options (Figure 2). Female part (T) is crafted from pure titanium and features replaceable nylon retention inserts that compensate for potential transfer inaccuracies between the impression, model, and clinical delivery (Figure 3).

This “erector set” allows totally passive support and retention for the prosthesis. If economics is a barrier to patient treatment, the system may be used as an alternative to two implants with a single connecting bar. At a later date, when the patient can afford two additional implants, the case can be converted to a four (or more) implant-supported prosthesis.

Conclusion

The SFI-Bar is relatively inexpensive compared to conventional gold castings and CAD/CAM options. The reduced amount of chair time relative to conventional or CAD/CAM techniques can also reduce costs. Precision-milled components provide a precise quality of fit. Due to this manufacturing process, the physical and mechanical properties of the component materials can be controlled, which is difficult with conventional casting methods.

This exclusive approach certainly has the potential to satisfy all of the requirements of an implant-supported overdenture at a reduced cost to the patient. This enables the profession to reach a much broader spectrum of appropriate patients.